1. Field of the Invention
The present invention relates to a camera for monitoring, and particularly relates to the camera for monitoring able to transmit a video signal to a master set by using power line communication (PLC).
2. Description of the Related Art
In recent years, a system having a power line communication function in in-home devices such as various kinds of home electric products, etc. is proposed within a home, etc. In this system, these in-home devices are monitored and controlled from a master set constructed by PC, etc. The above master set is accessed from the exterior through a public communication network. Thus, the in-home devices can be monitored and controlled from the exterior.
FIG. 3 is a view schematically showing the construction of the monitoring control system of the in-home device using the PLC in the prior art. The system of the prior art will next be explained by FIG. 3. In FIG. 3, reference numerals 31 and 32 respectively designate an indoor master set and a camera for monitoring. Reference numerals 33 to 35 designate in-home devices. Reference numerals 36, 37 and 38 respectively designate a PLC modem, a public communication network and a power line.
In the prior art shown in FIG. 3, the indoor master set 31, the camera 32 for monitoring and the in-home devices 33 to 35 are connected to the power line 38, and can be operated by receiving electric power from the power line. The PLC modem 36 is built in the indoor master set 31, or is externally attached to the indoor master set 31 so that the power line communication can be performed. Further, the indoor master set 31 has a function for performing the communication through the public communication network. The PLC modem is built in each of the camera 32 for monitoring and the in-home devices 33 to 35 so that the communication can be performed. For example, each of the in-home devices 33 to 35 may be constructed by a refrigerator, an air conditioner, a television set, a video recorder, etc.
The indoor master set 31 monitors the states of these in-home devices through the power line, and can control the operations of these in-home devices. Further, the indoor master set 31 can display a picture (dynamic image) from the camera 32 for monitoring in a display section, and can make a user see a state of the entrance of a house, etc. Further, the indoor master set 31 can control the photographing direction, the enlargement (e.g., the zooming of a lens) of a photographing range of the camera 32 for monitoring, etc. on the basis of commands of the user.
The indoor master set 31 as a monitoring terminal can communicate with another communication device through the public communication network 37 such as a telephone line, a portable telephone line, the Internet, etc. For example, the user carrying PDA, a portable telephone set, etc. and going out makes connection with the indoor master set 31 from the carried PDA, portable telephone set, etc. Thereafter, similar to the above case, the user can monitor the states of the in-home devices during the user's absence from a going-out place through the indoor master set 31 and can control the operations of these devices. Further, the user can control the operation of the camera 32 for monitoring and can receive a picture from the camera 32 for monitoring.
A technique for controlling the operation of the camera for monitoring and receiving the picture from the camera for monitoring by the power line communication is known as a typical technique of the above prior art (for example, see Patent Literature 1).
[Patent Literature 1]
Japanese Unexamined Published Patent Application No. H8-186809
Devices having the power line communication function are generally operated by the electric power from the power line, and the communication function is also fulfilled by utilizing the electric power from the power line. Therefore, when the supply of the electric power from the power line is interrupted by power stoppage, etc. in these devices, no original functions of the devices can be fulfilled and no power line communication can be also performed. In particular, in the case of the camera for monitoring explained above, when the supply of the electric power is interrupted by the power stoppage, no state of a monitoring area during the power stoppage can be known at all.